Eur J Appl Physiol (2007) 99:423–429 DOI 10.1007/s00421-006-0352-0
O RI G I NAL ART I C LE
Performance predicting factors in prolonged exhausting exercise of varying intensity Glenn Björklund · SoWa Pettersson · Erika Schagatay
Accepted: 8 November 2006 / Published online: 22 December 2006 © Springer-Verlag 2006
Abstract Several endurance sports, e.g. road cycling, have a varying intensity proWle during competition. At present, few laboratory tests take this intensity proWle into consideration. Thus, the purpose of this study was to examine the prognostic value of heart rate (HR), lactate (La¡1), potassium (K+), and respiratory exchange ratio (RER) performance at an exhausting cycling exercise with varying intensity. Eight national level cyclists performed two cycle tests each on a cycle ergometer: (1) a incremental test to establish VO2max, maximum power (Wmax), and lactate threshold (VO2LT), and (2) a variable intensity protocol (VIP). Exercise intensity for the VIP was based upon the VO2max obtained during the incremental test. The VIP consisted of six high intense (HI) workloads at 90% of VO2max for 3 min each, interspersed by Wve middle intense (MI) workloads at 70% of VO2max for 6 min each. VO2 and HR were continuously measured throughout the tests. Venous blood samples were taken before, during, and after the test. Increases in HR, La-, K+, and RER were observed when workload changed from MI to HI workload (P < 0.05). Potassium and RER decreased after transition from HI to MI workloads (P < 0.05). There was a negative correlation between time to exhaustion and decrease in Laconcentration during the Wrst MI (r = ¡0.714; P = 0.047). Furthermore, time to exhaustion correlated
G. Björklund · S. Pettersson · E. Schagatay Department of Natural Sciences, Mid Sweden University, Sundsvall, Sweden G. Björklund (&) National Winter Sport Center, Östersund, 831 25, Sweden e-mail:
[email protected]
with VO2LT calculated from the ramp test (r = 0.738; P = 0.037). Our results suggest that the magnitude of decrease of La¡1 between the Wrst HI workload and the consecutive MI workload could predict performance during prolonged exercise with variable intensity. Keywords
Cycling · Exercise · Lactate · Potassium
Introduction Road cycling has been a popular endurance sport since the late 19th century. During the last 50 years, the need for sophisticated race tactics and strategies has increased for succeeding in road cycling competitions. Contrary to marathon running where the athletes use a fairly constant pace throughout the competition (Costill 1970; Maron et al. 1976), the intensity during road cycling competitions involves both periods of extremely high as well as low work intensities (Lucia et al. 1999; Fernandez-Garcia et al. 2000; Padilla et al. 2001). To predict performance in endurance competitions, several physiological tests can be used. Common tests and variables for evaluation of endurance athlete’s capacity includes assessment of VO2max, lactate threshold, work-economy, and peak work rate (Coyle 1995; Basset and Howley 2000). At present, protocols for these physiological tests are mainly performed in a ramp or incremental workload fashion (Gore 2000). However, as exercise intensity in road cycling is characterized by a stochastic intensity pattern, a test protocol which takes this into consideration might give useful information e.g. about recovery processes that are important for performance.
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Only a few studies have examined the physiology behind a non-steady state exercise pattern with regard to workload (Ekelund and Holmgren 1964; Bot and Hollander 2000). A delayed onset of fatigue is among several other features associated with a strong performance in sport events; although, the cause of skeletal muscle fatigue is multifaceted (Fitts 1994) and still not fully understood. Moreover, some studies have shown elevated extracellular concentrations of both potassium (Sjøgaard et al. 1985; Medbø and Sejersted 1990) and lactate (Karlsson and Saltin 1970) at termination of strenuous exercise due to fatigue. It is debatable to what extent lactate is the cause of skeletal muscle fatigue (Nielsen et al. 2001; Kristensen et al. 2005). Furthermore, a linear heart rate proWle (Ahlborg 1967) as well as lactate (Bang 1936) response during prolonged steady-state exercise have been shown to be of prognostic value for performance. Although there are several tests that could predict performance in endurance sports, few take into account the variability of workload and give limited information regarding important recovery processes for performance. Therefore, the purpose of this study was to clarify the eVects of prolonged exercise with variable intensity and moreover to examine the prognostic value of heart rate (HR), potassium (K+), lactate (La¡1), and respiratory exchange ratio (RER).
Methods Subjects All volunteers (n = 8) were national level male cyclists (Table 1). Subjects were informed about the procedure of the test before they gave their written informed consent to participate in accordance with the Declaration of Helsinki. Furthermore, they were instructed not to eat for at least three hours before testing and not to consume any beverages containing caVeine on the day the tests were carried out. The research techniques and experimental protocol were approved by the Human Ethics Committee of Umeå University, Sweden. Incremental test In order to establish VO2max, subjects performed an incremental test which was continued to volitional fatigue on a SRM high performance bicycle ergometer (Schoberer Rad Messtechnik, Julich, Germany). Each subject adjusted the seat height, crank length and han-
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Eur J Appl Physiol (2007) 99:423–429 Table 1 Subject characteristics and laboratory measurements (n = 8)
Age Height (cm) Weight (kg) VO2max (l min¡1) VO2max (ml kg min¡1) VO2LT (%VO2max@LT) Wmax (W) W kg¡1
Mean (SD)
Min
Max
26(4) 183(7) 76(9) 4.7(0.5) 62(4) 69(6) 400(43) 5.3(0.3)
18 172 63 3.9 55 58 339 4.8
31 190 87 5.1 67 75 453 5.6
VO2LT, lactate threshold at % of VO2max; Wmax, maximal power output; W kg¡1 , maximal power output per kg body weight
dlebar position to match individual race position. The bicycle ergometer strain gauge was calibrated according to the manufacturer’s recommendation. The incremental test was performed according to Padilla et al. (1999) with a modiWcation of the start ramp to 85 W. Each work load was 4 min long with 35 W increments interspersed with 1 min periods performed at 50 W. Subjects were told to keep their cadence between 80– 90 rev/min throughout the test. The test was performed to exhaustion or terminated if the cadence fell below 70 rev/min. The cyclists breathed through the mouthpiece of an ergospirometric metabolic cart throughout the test (AMIS 2001, Innovision A/S, Odense, Denmark). Before each test, the ambient conditions were measured (Vaisala PTU 200, Vaisala Oyj, Helsinki, Finland) and gas analysers and inspiring Xow meter were calibrated. The gas analysers were calibrated with a high precision two component gas mixture (16.0% O2, 4% CO2, Air Liquide, Kungsängen, Sweden). Calibration of the Xowmeter was performed with a 3 l air syringe (Hans Rudolph, Germany) for low, medium and high Xow volumes. VO2max was calculated as a mean of the three highest measured values with a 10 s sampling frequency which would secure that true VO2 was obtained as shown by Johnson et al. (1998). During the 50 W work periods, a capillary blood sample of 20 l was taken from the Wngertip for lactate analysis. Each capillary sample was transferred to a 2 ml sample tube containing the analysis solution (Biosen 5140, EKF diagnostic, Magdeburg, Germany). All samples from each separate test were collected and analysed at the same occasion. Calibration of the lactate analyser was performed using a control solution of 4.8–6.4 mmol l¡1 and lactate standard of 12.00 mmol l¡1 VO2 lactate threshold (VO2LT) was set to the VO2 that corresponded to an increase in blood lactate concentration of 1 mmol l¡1 above
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baseline values. Heart rate was continuously recorded during the test with a telemetric transmitter (Polar S610, Polar Electro Oyo, Finland). Rate of perceived exertion (RPE) was determined with the 6–20 Borg-scale after each workload (Borg 1998). Maximal power output (Wmax) was determined as the highest workload the subjects could maintain for a complete 4 min work period. When the last workload could not be maintained for 4 min maximal power output was calculated as follows: Wmax = Wf + ((t/ 240) £ 35) (Kuipers et al. 1985), where Wf is the value of the last completed workload, t is the time (s) the last workload was maintained, and 35 is the diVerence in power (W) between the last two workloads. All subjects displayed a levelling oV in VO2 during the last part of the incremental test. Moreover, to further validate that the maximum eVort had been achieved, three criteria had to be met (1) RER > 1.10; (2) RPE > 17; and (3) La¡1 concentration >8 mmol l¡1 (Gore 2000).
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Venous blood samples during VIP A catheter (BD VenXon Pro, Becton Dickinson Infusion Therapy AB, Helsingborg, Sweden) was inserted in the left antecubital vein before the test. Venous blood samples were drawn before and immediately after the warm up period, right before the start of VIP, and during the last minute of each workload throughout the test. Also, during the Wrst HI (HI_1) and third HI (HI_3) workloads, blood venous samples were taken during the Wrst, second, and third minutes (Fig. 1). Two sample tubes were drawn at every occasion, one tube (3 ml) containing EDTA for analysis of La- (Biosen 5140, EKF diagnostic, Magdeburg, Germany), and the other tube (3 ml) for analysis of K+ and sodium (Na+) (Modular System, Hitachi Ltd., Tokyo, Japan). The catheter was Xushed with an isotonic NaCl infusion (Fresenius Kabi AB, Uppsala, Sweden) during the VIP. Data analysis and statistics
Variable intensity protocol The variable intensity protocol (VIP) was performed 24 or 48 h after the incremental test to avoid circadian diVerences. Subjects adjusted the bicycle ergometer as described above for the incremental test. Exercise intensity for the VIP was based upon the VO2max established in the incremental test. The VIP began with a 10 min warm up period at a workload corresponding to 50% of VO2max. Thereafter, the subjects performed a test protocol consisting of six high intense (HI) workloads of 90% of VO2max of 3 min each interspersed by Wve middle intense (MI) workloads corresponding to 70% VO2max for 6 min (Fig. 1). The test was terminated when the cyclist was not able to keep a cadence above 70 rev/min. Respiratory variables and heart rate were measured throughout the VIP as described above for the incremental test.
A one–way ANOVA with repeated measures was performed to determine diVerences in means of the physiological variables. A Fischer’s LSD post hoc test was used to identify diVerences revealed by the ANOVA. For correlation between time to exhaustion and physiological variables, a non-parametric two-tailed Spearman was carried out. Data comparison between ramp and VIP was performed using a paired Student’s t-test. SPSS 12.0 Software was used for statistic analysis (SPSS Inc., Chicago, IL). Data are expressed as means (SD). The level of signiWcance was set at P < 0.05.
Results Time to exhaustion during VIP Time to exhaustion (TTE) was 37 min (range 28– 48 min). All subjects (n = 8) completed at least four HI workloads. One subject was able to complete the whole VIP, i.e. all six HI workloads. Respiratory variables and heart rate during VIP
Fig. 1 Variable intensity protocol (VIP). Numbers represent workload as percent of VO2max. Arrows indicate when venous samples were taken
Oxygen uptake during MI- and HI workloads was 3.4(0.4) l min¡1 and 4.2(0.4) l min¡1, respectively: MI_1 3.4(0.4), MI_2 3.5(0.3), MI_3 3.5(0.3), HI_1 4.2(0.4), HI_2 4.2(0.4), HI_3 4.2(0.4), HI_4 4.2(0.5). The oxygen uptake did not diVer between the consecutive MI or HI periods (P > 0.05; Fig. 2). The RER increased when exercise shifted from MI to HI workload and
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the consecutive three HI (HI_2, HI_3, and HI_4) workloads (Fig. 3). K+ increased by 16(9)%, 18(10)%, and 18(11)% during HI_2, HI_3, and HI_4 workloads compared to the value during the last minute of HI_1 (4.8(0.3) mmol l¡1; P < 0.05; Fig. 3). Na+ increased after the third and fourth transition from MI to HI workload (P < 0.05). A decrease in Na+ concentration was detected going from HI to MI workload in the second and third transitions (P < 0.05). Time to exhaustion during VIP An inverse correlation (r = ¡0.714; P = 0.047) was found for lactate decrease concentration after the Wrst high intense workload (HI_1) and the following middle intense workload (MI_1) (Fig. 4). Incremental test compared to VIP No diVerence was seen in maximal heart rate between the incremental test and the VIP 191(7) bpm¡1 vs 191(10) bpm¡1. A diVerence was seen in maximal La¡ concentration between the incremental test and VIP at termination 13(2.7) compared to 8(2.9) mmol l¡1 Fig. 2 Oxygen uptake (VO2), respiratory exchange ratio (RER), and heart rate during variable intensity protocol (VIP). *P < 0.05 from the third minute of the Wrst high intense workload (HI_1). # P < 0.05 from the last minute of the Wrst middle intense workload (MI_1). No SD visible for the last HI (HI_6) as there was only one subject who completed the VIP
decreased when the exercise mode switched from HI to MI workload (P < 0.05). During the HI_1 workload RER was 1.05(0.06) and during the following three HI workloads (HI_2, HI_3 and HI_4) RER had increased by 2(4)%, 5(4)%, and 8(5)%, respectively (Fig. 2). Similarly, HR increased each time the intensity went up from MI to HI workload (P < 0.05). However, HR did not decrease when intensity returned to the HI workload (P > 0.05). Furthermore, HR was 164(11) bpm¡1 during HI_1 workload and increasing in the following three HI (HI_2, HI_3 and HI_4) workloads by 8(2), 13(2), and 15(5)% (P < 0.05) (Fig. 2). Blood variables during VIP During each transition from MI to HI workloads, La¡1 and K+ increased (P < 0.05). After both the HI_2 and HI_3 workloads transition to MI workloads, K+ had decreased (P < 0.05). The La¡1 concentration during the last minute of HI_1 workload was 2.8(1.3) mmol l¡1 and increased by 107(99), 143(119), and 173(132)% for
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Fig. 3 Lactate (La-) and potassium (K+) during variable intensity protocol (VIP). *P < 0.05 from the third minute of the Wrst high intense workload (HI_1). #P < 0.05 from the last minute of the Wrst middle intense workload (MI_1). No SD visible for the last HI (HI_6) as there was only one subject who completed the VIP
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Fig. 4 Correlation between change in lactate concentration between HI_1 and MI_1 and time to exhaustion (TTE). 95% Cl
(P < 0.05). A correlation between VO2LT and time to exhaustion for the VIP was detected (r = 0.738; P = 0.037) (Fig. 5).
Discussion Our aim was to identify factors that could be of prognostic value when predicting performance during prolonged variable intensity exercise and the results indicate that a decrease in blood La¡1 concentration following the Wrst high-intensity workload could be such a predictor. It is also of note that our results point that a low blood La¡1 concentration has no predictive value.
Fig. 5 Correlation between VO2LT and time to exhaustion (TTE). 95% Cl
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Potassium concentrations did not show a cumulative pattern for consecutive high intense work periods. Although La¡1 accumulated during high-intense workloads, all subjects independent of blood La¡1 concentrations decreased their RER below 1.0 during each middle intense workload. Furthermore, termination of the VIP occurred at signiWcantly lower La¡1 concentrations than the incremental test, even when methodological diVerences due to sampling sites are taken into consideration (Foxdal et al. 1990). The results also indicate that individual VO2LT could predict performance. However, during the high intense workloads, we found that these subjects with high VO2LT also displayed high La¡1 concentrations. This was somewhat unexpected considering that these subjects were exercising slightly above their La¡1 threshold. This could be explained by a higher rate of lactate release from the muscle. Some support for this notion could possibly be found in the presence of the lactate transport mechanisms. Previous studies have reported that La¡1 and H+ are transported between intracellular and interstitial compartments in a 1:1 ratio through membrane bound monocarboxylate transporters (MCT1, MCT4) (Wilson et al. 1998). The density of these transporters increases in the muscle membrane with an improved training status (Bonen et al. 1998; Dubouchaud et al. 2000). It has been reported that trained individuals are able to release La¡1 and H+ with a lower gradient over the muscle membrane (Pilegaard et al. 1999). These Wndings might explain the combination of high La¡1 concentrations along with high VO2LT during the Wrst high intense workload. The Wnding that TTE and VO2max displayed no correlation could indicate that the La¡1 eZux and reuptake are independent of peripheral aerobic training adaptations, which is in accordance with previous Wndings (Green et al. 2002). Potassium concentration observed at termination of the VIP test was approximately 6 mmol l¡1, which is lower than what has been reported in previous studies (Sjøgaard et al. 1985; Medbø and Sejersted 1990; Nielsen et al. 2004). Although the monocarboxylate proteins contain the predominant pH intracellular regulating system (Juel 1996), a possible explanation between lactic acid accumulation and K+ re-uptake could be the inXuence of the Na+/H+ exchanger. Kristensen et al. (2005) proposed that a large pH gradient across the sarcolemma is not a necessity but might contribute to an increased activity of the Na+/H+ exchanger. As the proton is excluded from the cell, sodium is added in the intracellular compartment. An inXux of Na+ has been shown to stimulate the Na+/K+ pump (Buchanan et al. 2002).
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This in turn could result in a faster K+ uptake. The degree of re-uptake is coupled to an increase in Na+/K+ ATPase catalytic subunits (Nielsen et al. 2004), which is a training induced adaptation. Furthermore, K+ has also been reported to display a fast t½ (
